<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
  <div id="app">
    {{msg}}
    <span v-once>{{msg}}</span>
  </div>

  <script src="./vue.js"></script>
  <script>
    /* 
      如果给标签添加了v-once那么该标签中只有第一次数据会被渲染出来，再次改变数据后，页面上数据不会再次改变
    
     */
    const app = new Vue({
      el: '#app',
      data: {
        msg: 'Hello World'
      }
    })
  </script>
</body>
</html>